1. Field of the Invention
The present invention relates to a control method of a magnet type fan clutch which controls rotation of a cooling fan to be mainly applied to an internal combustion engine for vehicles, and more specifically to a control method of a magnet type fan clutch, which is configured in such a manner that a magnet coupling and an electromagnetic clutch are integrated with each other and the magnet coupling is controlled so as to be turned on and off by the electromagnetic clutch.
2. Description of Related Art
As a magnet type fan clutch which controls rotation of a cooling fan to be applied to an internal combustion engine for vehicles, in JP-A-9-119455, a viscous fluid joint which transmits an output drive torque to a radiator cooling fan by a driving torque from an engine for vehicle and its control method are disclosed. This viscous fluid joint takes a system for fluctuating an oil supply amount when a valve is opened or closed due to transformation of a bimetal responding to a temperature of a radiator passing wind and changing a rotation of a fan. To explain it more in detail, an object of this system is to prevent a fan noise and a heat of slip at a low idle condition when a vehicle is stopping and this system is constituted by steps of detecting a rotational rate of a vehicle engine, comparing its actual measurement value with a limited value that has been set in advance, detecting a rotational rate of a radiator cooling fan when the rotational rate of the engine is lower than the limited value, comparing a fan rate with a fan rate limited value that has been decided in advance, and correcting an input signal in order to move a valve member to a closed position when the fan rate is higher than the limited value.
However, according to the control method of the viscous fluid joint of a system that the valve is opened or closed by transformation of the bimetal reacting to a temperature of a radiator passing wind to fluctuate the oil supply amount and change the fan rotation, it is not possible to make the temperature of an engine cooling fluid deciding an engine cooling performance into a direct control object, so that this involves disadvantages such that a loss of horsepower is generated due to an unnecessary fan rotation, a lower fuel economy is caused, a good fan rotation of cooling of a condenser of an air condition (A/C) cannot be maintained, and a fan noise due to the unnecessary fan rotation at an acceleration time cannot be reduced or the like.
Therefore, in order to solve the disadvantage of a cooling control method depending on the above-described radiator passing wind temperature, the present applicant proposed an external control system fan clutch capable of improving an engine performance and a fuel economy, improving a cooling performance of an air conditioner (A/C) condenser, and reducing a fan noise by externally controlling the fan clutch in advance (refer to U.S. Pat. Nos. 6,634,476 B2, 6,811,009 B2, JP-A-2003-156072 or the like). This external control system fan clutch is configured in such a manner that the magnet coupling and the electromagnetic clutch are integrated with each other, the fan is attached to the magnet coupling side, and the magnet coupling is controlled so as to be turned on and off by the electromagnetic clutch. Specifically, for example, the external control system fan clutch is configured by a rotatable electromagnetic clutch comprising a clutch rotor that is supported by a driving shaft and an excitation coil supported by the exterior is incorporated therein and an armature attached to a circular disk rotatably supported by the driving shaft via a bearing device; and a magnet coupling, which is rotatably supported by the driving shaft via the bearing device, and has a hysteresis material or a conductor that is attached to the circular disk so as to be opposed to a permanent magnet rotator to which outer circumference a fan is attached and the permanent magnet at a slight gap, and the permanent magnet rotator and the circular disk are rotated integrally or relatively due to the action between the permanent magnet and the hysteresis material or the conductor. The magnet coupling is ON and OFF controlled by the electromagnetic clutch.
The magnet type fan clutch of such a configuration can control a magnet coupling, namely, a fan rotation by ON and OFF controlling the electromagnetic clutch. In addition, the electromagnetic clutch is ON and OFF controlled in conjunction with a temperature of cooling water, throttle opening, an engine rotation rate, an accelerator (throttle) opening and a switch of the air conditioner, so that the magnet type fan clutch has an excellent advantage such that it can stably control the fan rotation with a high degree of accuracy.
However, according to a binary control with an engine cooling fluid temperature used as a control parameter, when the engine cooling fluid temperature is near a set threshold, ON and OFF of the clutch is frequently caused and a loss of a horsepower, a noise, and wear of a friction plate of the clutch or the like become problems. For example, with respect to a relation between fan rotation rate and horsepower consumption when the clutch is changed temporarily from OFF to ON, inertia horsepower of the fan and the fan clutch (an inertia moment the fan rotation acceleration) are generated several times upon a stationary fan.